Once infected the rabies virus will slowly work its way up through the nerves to the brain where it will cause severe encephalitis and then certain death. Its a horrible way to die.
The time between bite and infection to appearance of symptoms after it reaches the brain will depend on where the bite is. If its in a toe or a finger it will take much longer for the symptoms to occur as opposed to if bitten on neck etc because the virus needs to travel a longer path to the brain.
If vaccinated before the occurrence of symptoms (best within 6 days of bite) the vaccine is 100% effective.
Rabies can manifest itself even months or years after the bite. So if you have even the slightest doubt about the slightest scratch from an animal best to get vaccinated.
If bitten or scratched the victim should immediately cleanse the wound for 5 minutes with soap and running water which will reduce the amount of virus in the wound, before going to the hospital.